1. Field of the Invention
The present invention relates to a method for correcting alignment to make a relative alignment between patterns in a plane direction for forming a plurality of patterns in manufacturing a semiconductor device, a method for manufacturing a semiconductor device and a semiconductor device.
2. Description of the Background Art
Now discussion will be presented on alignment with reference to a conceptional diagram of FIG. 24. A plane 3a has patterns 1a alignment marks 2a to 2d. A plane 3b has patterns 1b and alignment marks 2e to 2h. The patterns 1a and 1b are formed on wafers and made of silicon compound, metal or the like. The alignment marks 2a to 2d are formed simultaneously with the patterns 1a. The alignment marks 2e to 2h are formed simultaneously with the patterns 1b. An operation to relatively align positions of two objects, such as the planes 3a and 3b, is referred to just as "Alignment".
In a process for manufacturing a semiconductor device, several major steps are performed to manufacture the semiconductor device. The major step is a unit of a plurality of steps for forming a pattern (e.g., a film-formation step for forming a film on a wafer, a resist coating step for coating a resist, an exposure step, a developing step, an etching step for patterning a film and so on).
FIG. 25 is a conceptional section of a semiconductor device. The semiconductor device of FIG. 25 is obtained through seven major steps, and patterns 301 to 307 are formed through the seven major steps, respectively.
The alignment is required in the exposure step. In the exposure step, actually, an alignment is performed to relatively align the positions of a reticle and a wafer. Among apparatuses for exposure and alignment is a step-type projection aligner (hereinafter, referred to as "stepper").
FIG. 26 is a block diagram of a manufacturing system 10 for manufacturing a semiconductor device. The figure shows steppers 4 as mentioned above, overlay checking devices 5, a production control system body 6 for performing a production control which includes an alignment correction unit 6a and a database 6b, semiconductor manufacturing devices 7 and reference terminals 8 connected to the production control system body 6 for making reference to the database 6b. In this system, there are a plurality of steppers 4 and semiconductor manufacturing devices such as a sputtering device and an etching device.
Among patterns which are aligned by the stepper 4, there exist a shear despite of the alignment. This is due to a mechanical error of the stepper, a manufacture error of the reticle and so on. The stepper 4 is given a correction value for resolving the shear (hereinafter, referred to as "stepper correction value"). On the other hand, the overlay checking device 5 detects the shear and calculates a correction value for resolving the shear (hereinafter, referred to as "OCCV (overlay checking correction value)").
The production control system body 6 controls data on alignment (hereinafter, referred to as "alignment data"). The alignment data include the OCCV, the step correction value, the type of wafer (lot No., product No. and the like), date of alignment, processing, production history and so on. The alignment data are stored in the database 6b.
The alignment correction unit 6a is one of functions of the production control system body 6 and calculates the stepper correction value.
FIG. 27 illustrates a constitutional conception of the stepper 4. In this figure shown are a wafer stage WST on which a wafer 20 is mounted, a reticle stage RST on which a reticle 30 is mounted, an illumination system ILS, a lens system PL, a stepper correction value for wafer component 22 and a stepper correction value for shot component 33.
The stepper 4 receives the stepper correction value. The stepper correction value includes the stepper correction value for wafer component 22 and the stepper correction value for shot component 33.
The stepper correction value for wafer component 22 is a value which is set to move the wafer. The stepper correction values for wafer component 22 includes stepper correction values for offsets X and Y (base line), scalings X and Y, X-Y orthogonality and wafer rotation. The wafer stage WST travels in accordance with the stepper correction values for wafer component 22.
The stepper correction value for shot component 33 is a value which is set to change an image 34 projected on the wafer 20 from the illumination system ILS through the reticle 30. The stepper correction values for shot component 33 include stepper correction values for shot rotation, magnification and the like. The image 34 varies with the stepper correction values for shot component 33. In more detail, as to the shot rotation, the reticle stage RST rotates about a center axis 32 to rotate the image 34. As to the magnification, the image 34 is enlarged or reduced by the lens system PL and the like.
The production control system body 6 processes the wafer as follows. Herein, an alignment of the plane 304 of FIG. 25 will be taken as an example. The processing is performed according to a flowchart of FIG. 28.
First, the production control system body 6 transports a wafer to be processed to the stepper 4. When the wafer reaches the stepper 4, the alignment correction unit 6a calculates the stepper correction value (Step S901 of FIG. 28).
The production control system body 6 sets the stepper correction value obtained by calculation to the stepper 4 (Step S902).
The stepper 4 performs an alignment (Step S903).
After completing the alignment, the production control system body 6 registers the stepper correction value in the database 6b to control the stepper correction value. Further, the wafer is transported from the stepper 4 to the overlay checking device 5 (Step S904),
The overlay checking device 5 detects a shear between the pattern 304 and the pattern 303 immediately therebelow with the positions of the alignment marks (Step S905). Further, the device 5 calculates the OCCV to resolve the detected shear (Step S906).
Subsequently, the production control system body 6 collects the OCCVs from the overlay checking devices 5 (Step S907). The system body 6 stores the collected OCCVs in the database 6b and controls them (Step S908).
Further, the production control system body 6 transports the wafer to be processed to the semiconductor manufacturing device 7, as needed, where sputtering, etching and the like are performed.
Through the above steps, the production control system body 6 processes the wafer.
Next, a method for correcting alignment to calculate the stepper correction value in the background art will be discussed with reference to FIGS. 29 and 30. It is assumed that the stepper correction value set in the Step S902 is +1 and the OCCV (which herein corresponds to the shear) detected in the Step S906 is -2 in this alignment performed in the major step. Therefore, as shown in FIG. 30, if the stepper correction value is set at +3 in the alignment of the next major step, it is expected that the OCCV should be 0. The calculated difference between the stepper correction value and the OCCV is referred to as "true shear". Specifically this is expressed as, EQU true shear=stepper correction value-OCCV . . . (1)
Shorter time lag between the present alignment and the next alignment causes smaller true shear.
As the time lag becomes longer, the true shear becomes larger. Then, the production control system body 6 controls a trend of the true shear in a major step as shown in FIG. 31, and the alignment correction unit 6a calculates a mean value of true shears at the time points P1 to P3 in the same major step as the stepper correction value to be set in the next major step tx.
Thus, in the background-art method for correcting alignment, the stepper correction value for wafer component is corrected to align a pattern with a pattern immediately therebelow, like the patterns 304 and 303.
For size reduction of a semiconductor device, a small tolerance (specification) of the shear between patterns is required. In recent, as the size of a semiconductor device becomes smaller, too much smaller tolerance has been established than ever. The shear between patterns used to be within specification if the stepper correction value for wafer component was corrected. With establishment of too much smaller tolerance, however, there recently arises a problem that some shear out of specification is caused when the background-art method for correcting alignment is performed, and an improvement in precision of alignment is required.